Architectural Ceramics

Author: Hans-Jürgen Schwarz
English Translation by Sandra Leithäuser
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Abstract

Typical deterioration patterns for architectural ceramics are discussed and explained.

Decay patterns of architectural ceramics

Deterioration of brickwork

Salt-induced damage to bricks is common.

Damage to bricks can appear as follows:

Glazed architectural ceramics

The glaze on building ceramics prevents the transport of moisture and salts. Often however, the glaze shows "crazing" (a fine network of fissures or cracks) allowing moisture transport through it. And therefore, if salts are present, they will crystallize around these fissures as well as below the glazing around them, leading to their spalling.

Some examples of salt-contaminated glazed building ceramics are shown here.

Flaking

• Decay pattern on a brick of the St. Jakobi Church in Perleberg
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  Figure 1: The scaling surface of a damaged brick, caused by crystallizing salts.

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  Figure 2: Photo micrograph of a thin section in polarized light. The gray parallel crystals are gypsum.

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  Figure 3: Photo micrograph as Fig 2 with crossed polarizers. It is clearly visible that, on the one hand gypsum is causing the damage to the brick, but on the other hand it acts like an adhesive/ cement, holding the flaking pieces in place. With the removal of the gypsum the original substance of the brick would be lost.

Weathering

• Damage to a building in Lüneburg
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  Figure 4: Salts causing damage to a molded brick

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  Figure 5: Salt action under a coat of paint, scaling and disintegration of the brick

Efflorescences

• Efflorescences on architectural ceramics
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  Figure 6: Salt efflorescence on a flagstone

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  Figure 7: Encrustations on a pillar formed by carbonate salts and caused by the leaching of cement slurry injections.

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  Figure 8: Crystallizing salts accentuate the craquele on a glazed tile. Gradually, the salts will damage the glaze.

crystallization of a dissolved salt